1. Field of the Invention
This invention relates to cutter and/or stripper apparatus and more particularly for cutter and/or stripper apparatus for objects having relatively small cross sections.
2. Description of the Prior Art
In certain applications there is a need to cut and/or strip objects with relatively small cross sections. The need is even more acute particularly in applications for cutting and/or stripping objects that are easily deformable or distortionable but it is desired to keep the objects from being deformed or distorted during the cutting and/or stripping operation(s).
One such application arises in the manufacture of certain type inserts for printed circuit boards, where the inserts and/or boards are precision components. One particular insert has a thin walled conductive hollow core and a concentric outer insulative sleeve or coating. The insert is made from flexible tubing stock consisting of a metal, e.g. copper, hollow core and an outer conformal dielectric coating or sleeve. The stock is cut into sections or pieces, and a portion of the sleeve is cut and stripped from one end of each section to form an insert.
The insert is used in connection with the repair of defective plated through holes, i.e. via holes, in certain laminated multilayer printed circuit boards. After predrilling the defective hole to remove its associated plating, the insert is inserted in the via hole with the non-stripped part being located within the hole and with the stripped part, herein sometimes referred to as the extension, protruding outwardly from the hole on one side of the board. The outer diameter of the insert and the diameter of the drilled out defective hole are compatible so as to effect a snug-like fit between the two. The dielectric sleeve insulates the section's conductive core from any inner plane conductive members of the board which may be adjacent to the wall of the hole.
With the aid of a special tool, the stripped extension is then formed into a substantially planar flange on an annular pad which was previously formed as part of the printed circuitry on the aforementioned one side of the board concentrically about the periphery of the hole. On the opposite side of the board, a connector, which is a slightly modified configuration of the bifurcated connector type that is described in U.S. Pat. No. 3,915,537 assigned to the common assignee herein, is next inserted by the pretinned base of its stem through the opening of the hollow core of the insert. A reflow solder process bonds the inserted stem base to the insert's core and the insert's flange to the aforementioned pad of the board.
Heretofore, the cutters and strippers of the prior art were not conducive to providing cutting and stripping operations for objects having small cross sections such as, for example, the aforementioned thin wall tubing. It was found that conventional cutters and strippers subjected the object to deformation and distortion. For example, in the aforedescribed application, the inserts would easily be crushed during the cutting and stripping operations associated with the conventional cutters and strippers. As a result, the distorted or deformed inserts were not insertable in the via holes and/or the stem bases of the aforementioned connectors were not insertable in the deformed or distorted cores. Moreover, the apparatus of the prior art were susceptible to providing skewed and ragged cuts in the object, i.e the core and/or insulation.
Cutters and strippers of the prior art, of which we are aware, are not generally applicable to cutting and stripping objects of small cross section for many reasons. One reason is that in many applications the prior art apparatus are intended to cut or strip relatively gross type objects which have relatively liberal tolerance requirements. These prior art apparatus are thus generally not concerned with the accuracy and reliability required for the cutting or stripping of objects which have high tolerance requirements and/or which also may be precision components as well, and hence are incapable of doing so. This is particularly true where the components are ultra-miniature electrical/electronic components requiring precision dimensions and shapes for mechanical and/or electrical compatibility with the ultimate system in which they are to be incorporated. Examples of such prior art apparatus are described in U.S. Pat. Nos. 1,306,588, 2,112,396, 3,540,333 and 3,772,945.
These last mentioned patents are also typical of apparatus where the cutter mechanism is radially mounted on a rotatable or rotary head relative to the axis of rotation of the head. In this type of apparatus, referred to herein as rotary head cutters or simply as rotary cutters, the object to be cut is positioned within the head in coincidence with the axis of rotation such that as the head is rotating the orbiting cutting mechanism performs the cutting operation. Heretofore, in the prior art complex mechanical systems were required for movement of the the cutter mechanism toward and/or away from the object, and the movement is done in a constant, i.e. non-variable, or an uncontrolled manner.
Thus, referring to U.S. Pat. No. 1,306,588, the wire stripper apparatus thereof cuts the insulation at one end of an insulated conductive wire and from which end the insulation is to be stripped. More particularly, in the apparatus of U.S. Pat. No. 1,306,588, two straight edge cutters, i.e. chisel type cutter blades or knives, are each part of one of the two independent dual mechanical linkage systems. Each system moves its particular one blade in a radial direction and is mounted with its particular blade on a common spindle head. The spindle head has a central opening through which is positioned the end of the wire having the uncut insulation to be stripped. In each linkage system, the blade is pivotally mounted to one side of a lever, which is in turn pivotally mounted to the head. The blade has an elongated guiding slot through which passes a guide screw affixed to the head. A bias spring is affixed to the screw and to the lever on the other side of the lever pivot. A centrifugal weight is carried at the end of the lever that is on the same last mentioned side of the lever pivot.
In operation, when the spindle head is stationary, each bias spring positions the respective lever about its pivot so as to maintain the particular centrifugal weight toward and the particular cutter blade away from the central opening and hence away from the end of the insulated wire. When the head is rotating, in response to centrifugal force the weight of each linkage system moves in a radially outward direction overcoming the spring bias and thereby causing the lever to pivot and the blade to move in a radially inward direction via the coaction of the guide slot and screw. Thus, the cutting edges of the two blades are advanced toward each other by their respective linkage systems. Upon contacting the insulation, the cutting edges of the two orbiting blades circumferentially score the insulation on opposite sides of the wire resulting from the combined orbital motion of the blades caused by the rotating head and the continuing inward radial advancement of the blades caused by their respective linkage systems. With the aid of appropriate stops, the inward radial advancement is stopped when the insulation is completely severed through and thereafter the severed insulation piece is removed or stripped by pulling the wire to expose the portion of the inner conductor from which the piece has been stripped.
Prior art apparatus such as the type described in U.S. Pat. No. 1,306,588 has several limitations which do not make it conducive to cutting objects of small cross section such as, for example, the aforedescribed precision inserts. For one thing, the end of the wire being stripped is maintained free, i.e. unsupported, thereby making it vulnerable to deflection and hence a concomitant misalignment in its orientation with respect to the two cutter blades thereby resulting in a skewed and/or ragged cut of the insulation and/or undesirable cutting of the wire conductors. In addition, without precise diametrical and planar alignment of the two blades and/or synchronized movement of the two blades, the wire is subject to deflection if contacted by one blade before being contacted by the other blade and hence results in the insulation being skewed cut and/or ragged cut as well as undesirable cutting of the conductors. Hence, such apparatus is generally unreliable for cutting objects with small cross sections and/or for making clean, high tolerance, precision cuts. Its reliability is further compromised because of the difficulty in obtaining dual linkage systems with precisely matching counterpart elements and characteristics and/or the relatively large number of moving parts required by the dual linkage system, which by the way increases the cost of making and assembly of such systems and their parts. Moreover, the apparatus requires that the wire to be stripped must be fed thereto while the head is stationary so that the cutter blades are not obstructing its passage. Hence, it is not conducive for adaptation to mass production as it requires intermittent stopping and starting of the head rotation thereby increasing time and cost in processing the wire therethrough. In addition, another mechanism is required to cut the wire in a prior operation thereby further subjecting the object to additional chances of being deformed or distorted.
U.S. Pat. No. 2,112,396 is another example of a rotary cutter. It has a disc knife and two back up rollers, the three being symmetrically positioned about the central axis of the head. A shift mechanism shifts the knife and two rollers in a radial inward direction to bring them into contact with the tube stock to be cut. The knife and two rollers are mounted on individual blocks. Each block has an individual cam follower pin affixed to it. An outer concentric shiftable gear, with internal teeth coacting with four symmetrically spaced pinion gears, when shifted in the proper direction rotates an inner concentric gear with external teeth that also coact with the pinion gears. The inner gear carries three cam slots, each of which coacts with one of the cam follower pins. Thus, when the external gear is shifted and the internal gear in response shifts a corresponding predetermined angle, the resultant camming action moves the blocks, which are positioned in radial slots, in a radially inward direction. As a result, the knife and rollers move in a likewise radial inward direction from their retracted positions relative to the centrally aligned tube stock to positions of contact with the tube stock.
However, while this is being done, the head is not rotating. Once contact is made and the knife thereby makes an initial incision in the tube stock wall, the rotation of the head is initiated. The head is rotated at a high speed and orbits the contacting blade and rollers around the tube wall causing them to rotate on their own respective axes as well. The tube wall is circumferentially cut by the knife until a piece is completely severed from the stock. However, in the cutter of U.S. Pat. No. 2,112,396, centrifugal force is undesirable because it tends to react on the blocks in a radially outward direction and thus pull the knife and rollers away from the stock thereby adversely affecting the cutting operation. To overcome this, unbalanced weighted levers are required and arranged to exert a centrifugal force in opposition to that being exerted on the blocks.
Again, the rotary cutter of U.S. Pat. No. 2,112,396 is not conducive for cutting objects of small cross section such as thin wall stock. For one thing, the use of three contact elements, i.e. the knife and two rollers, establishes a finite limit as to the size of the tube stock that can be fitted in the space defined between the three elements. That is to say, the smallest space defined between the three elements occurs when the three elements are in contact with one another. When the three are in such contact, a diameter size is established by the circle defined by the three respective midpoints located on the respect circumferential peripheries of the three contacting elements, which midpoints lie between the three respective points of contact of the three elements. Hence, any stock with a nominal diameter size equal to or less than the aforedescribed established size cannot be cut with the apparatus of U.S. Pat. No. 2,112,396.
Moreover, if the tube stock being cut by the apparatus of U.S. Pat. No. 2,112,396 is not rigid but is flexible, then without precise synchronized movement of the knife and two rollers, the tube stock is subject to deflection, resulting in skewed and/or ragged cuts and thereby making the apparatus unreliable. Its reliability is further compromised because of the difficulty in obtaining knife and roller systems with precisely matching counterpart components and characteristics and/or the relatively large number and complexity of moving parts required by such systems, which also by the way increases the cost of making and assembly of such systems and their parts. Moreover, because the head is required to be stationary while the cutter knife and rollers are being positioned to contact the stock, it is therefore not conducive for adaptation to mass production as it requires intermittent stopping and starting the rotation thereby increasing time and cost in processing the stock therethrough.
For similar reasons, the tube cutters of U.S. Pat. Nos. 3,540,333 and 3,772,945 are also inadequate for cutting objects with small cross sections and in particular objects such as the aforedescribed precision inserts. In U.S. Pat. No. 3,540,333, three orbital cutter wheels are carried on lever arms pivotally mounted on a rotating wheel and are brought into contact with a three ply paper tubing stock by a cinch cable encircling pulleys on the lever arms. The apparatus requires concurrent rotation of the head, counter rotation of the tubing, and linear motions of the head and tubing in the same direction, which linear motions must also be synchronized with the linear motion of the tubing which feeds it to the apparatus.
The disk cutter blade and two non-cutting roller disks of U.S. Pat. No. 3,772,945 are mounted on individual slides that are spring biased in an outwardly radial direction. A linear actuated camming member is required to shift the three elements, i.e. the blade and two roller disks, radially inward so as to contact the tube, as the three elements orbit about the tube.
Thus, the rotary cutters of these last two mentioned patents likewise suffer from the same deficiencies of the first two mentioned patents. Without precise synchronized movement of the three contact elements, the tube is subject to deflection and hence to being skewed and/or ragged cut, which are not tolerable in high tolerance cut type applications such as the aforedescribed precision inserts. Hence, the apparatus of these last two mentioned patents are not generally reliable. Moreover, in the case of the apparatus of U.S. Pat. No. 3,540,333, if the aforedescribed linear motion of the tubing should get out of synchronization with the feed advance motion, the tubing is subject to deflection, distortion and skewed and/or ragged cuts.
The reliability of the apparatus of these last two mentioned patents is still further compromised because of the difficulty in obtaining three element contact systems, i.e. the lever system of U.S. Pat. No. 3,540,333 and the cam system of U.S. Pat. No. 3,772,945, with precisely matching counterpart components and characteristics and/or the relatively large number and complexity of moving parts required by such apparatus, and which it again is pointed out increases the cost of making and assembly of such systems and their parts.
For another thing, as explained previously with respect to the three contact element system of U.S. Pat. No. 2,112,396, each of the respective three contact element systems of U.S. Pat. Nos. 3,540,333 and 3,772,945 likewise establishes a finite limit as to the diameter size of the object that can be fitted in the space defined between the three elements, and any object with a diameter size less than or equal to the finite limit is unable to be cut.
Moreover, in none of the aforedescribed prior art apparatus is a variable control provided for the radial movement of their respective moving elements.